1. Field of the Invention
The present invention relates to an apparatus for detecting a leakage of heavy water in a nuclear reactor system and a method for detecting a leakage of heavy water using the same, and more particularly, to an apparatus for detecting a leakage of heavy water in a nuclear reactor system capable of sensitively monitoring a leakage of heavy water within a nuclear reactor system by sampling the air or by sampling a secondary side of a steam generator in real time by taking an air test sample around a pressure tube or a delayed neutron tube of the nuclear reactor system or a test sample from the secondary side of the steam generator, and detecting and measuring the concentration of mixed heavy water molecules by using the laser absorption spectroscopy, and a method for detecting a leakage of heavy water using the same.
2. Description of the Related Art
A leakage of heavy water in nuclear energy (or atomic power) facilities has a direct connection with a leakage of radioactivity, critically affecting the stability of a nuclear energy production facility. In particular, because a heavy water nuclear reactor system is made up of 380 or more pressure tubes, and numerous pipes are installed in a complicated manner, the detection and monitoring of a heavy water leakage is crucial.
The related art method for detecting a leakage of heavy water in a nuclear reactor system includes an infrared spectrometry method, a radiation monitoring method, a mass spectroscopy method, and the like.
The infrared spectrometry method is a heavy water leakage detection method using the qualities of components of a material that vibrate while absorbing a particular wavelength when irradiated by an infrared ray.
Namely, when an infrared ray irradiates the material, its components vibrate while absorbing a particular wavelength of the infrared ray, and as a result, as an infrared spectrum measured after the irradiation has a pattern in which absorption has occurred in a particular wavelength region causing such molecular vibration, qualitative analysis and quantitative analysis of the material can be possibly performed based on such spectrum analysis.
Heavy water, (D2O), within the nuclear reactor system, refers to a combination of two heavy hydrogen atoms (2H or D) having a mass number of 2 with oxygen (O), and light water, (H2O) refers to a combination of two hydrogen atoms (1H) having a mass number of 1 with oxygen (O).
When heavy water within the nuclear reactor system leaks and meets light water, the heavy water is mostly changed from D2O to mixed heavy water (HDO) due to collision reaction between heavy water and light water. The infrared spectrometry determines whether or not heavy water has leaked by measuring the density of heavy water in light water by using the difference between the infrared absorption characteristics of the heavy water and that of the light water (Seung Yeol Cho, et al. Vibrational Spectroscopy 31, 251 (2003)). The infrared spectrometry method can employ FT-IR (Fourier Transform Infrared) equipment commercially on sale, does not require to pre-process a test sample, and its operation is easy. However, this method is disadvantageous in that measurement sensitivity is low, analysis of an air test sample is not possible, and it is not possible to measure heavy water leaked into the air.
The radiation monitoring method is mainly concerned with measuring beta radiation radioactivity having weak energy. In this method, radioactivity caused by tritium (3H or T) leaked to a secondary side with heavy water is measured within light water to monitor whether or not the heavy water has leaked.
Tritium used for a heavy water leakage detection method using a liquid scintillation counting method, which is a radioisotope of hydrogen having a mass number of 3, is a pure beta-emitting radionuclide having a half-life of 12.35 years and emitting beta rays with energy of an average 5.7 KeV.
The tritium is generated as the heavy hydrogen present in a great quantity of heavy water present in a primary side is reacted with a neutron, and the density of the tritium generated thusly in the primary side increases as an operational time of nuclear power plants increases. Thus, it may be determined whether or not the heavy water within the primary side has leaked to the secondary side by monitoring whether or not the density of the tritium within the secondary side increases.
However, although the liquid scintillation counting method has a high sensitivity in the heavy water leakage measurement, it disadvantageously incurs a great deal of maintenance and repair cost, generates a harmful waste scintillation liquid, and is extremely difficult to utilize as a real time monitoring apparatus.
The mass spectroscopy method, which determines whether or not heavy water has leaked by deoxidizing water molecules to generate hydrogen molecules and measuring an isotope ratio of H and D of hydrogen molecules, is advantageous in that it has a high level of measurement sensitivity, but it requires a high-priced, high resolving power mass analyzer of a double focusing magnetic sector type having a mass resolving power of 2000 or higher, requires a complicated test sample preprocessing procedure for deoxidizing HDO molecules into HD molecules, and is not suitable for a real time monitoring apparatus.
Besides the above-mentioned methods, whether or not heavy water has leaked may also be determined by measuring an acoustic wave generated when heavy water has leaked in the air (P. Kalyanasundaram, et al. International Journal of Pressure Vessels and Piping 36, 65 (1989)). However, this indirect acoustic wave measurement method has difficulty in discriminating between acoustic wave caused by a leakage of heavy water and ambient noise, and has a low level of sensitivity. In addition, because this method is a contact type method, there is a limitation in its employment, and further, it cannot detect a leakage of heavy water from a steam generator.